Due to recent economic growth and changes in dietary habits, etc., the incidence of metabolic syndrome-associated diseases including various diseases such as obesity, hyperlipidemia, hypertension, arteriosclerosis, hyperinsulinemia, diabetes, and liver diseases is rapidly increasing. These diseases may occur independently but in general they mostly occur in close relationship with each other, being accompanied by various symptoms.
In particular, according to the World Health Organization (WHO), more than one billion adults are overweight worldwide, among them over 3 million are clinically obese, and 250,000 people die every year in Europe and more than 2.5 million people worldwide die every year due to overweight-related diseases.
Overweight and obesity are responsible for increasing blood pressure and cholesterol levels and causing or worsening various diseases, such as cardiac diseases, diabetes, arthritis, etc. In addition, the problem of obesity is also becoming a major cause in the increased incidence of arteriosclerosis, hypertension, hyperlipidemia, or heart diseases in children or teenagers as well as in adults.
Although obesity is a severe condition that causes various diseases worldwide as described above, it is thought to be overcome by individual effort, and it is also believed that obese patients lack self-control. However, obesity is not easy to treat, because it is a complex disease associated with the mechanisms of appetite control and energy metabolism. Accordingly, the treatment of obesity requires not only the efforts of obese patients, but also a method capable of treating abnormal mechanisms associated with appetite control and energy metabolism. Thus, efforts have been made to develop drugs for treating the abnormal mechanisms.
As a result of these efforts, drugs such as Rimonabant® (Sanofi-Aventis), Sibutramin® (Abbott), Contrave® (Takeda), Orlistat® (Roche), etc have been developed, but they have the disadvantages of serious adverse effects or very weak anti-obesity effects. For example, according to a report, Rimonabant® shows a side-effect of central nervous system disorder, Sibutramine® and Contrave® show cardiovascular side-effects, and Orlistat® shows only about 4 kg of weight loss when taken for one year. Accordingly, there are no therapeutic agents for obesity which can be prescribed safely for obese patients.
Many extensive studies have been made to develop novel therapeutic agents for obesity which can resolve the problems of the conventional anti-obesity drugs. Recently, glucagon derivatives have received much attention. Glucagon is produced by the pancreas when blood glucose levels drop as a result of other medications or diseases, or hormone or enzyme deficiencies. Glucagon sends a signal for glycogen breakdown in the liver and a subsequent glucose release and plays a role in increasing blood glucose levels to a normal range. In addition to the effect of increasing the blood glucose levels, glucagon suppresses appetite and activates hormone-sensitive lipase of adipocytes to facilitate lipolysis, thereby showing an anti-obesity effect. However, the use of glucagon as a therapeutic agent has been limited because it has a low solubility and it is precipitated at a neutral pH.
Accordingly, the glucagon with improved properties alone can be effectively used for the treatment of severe hypoglycemia, nonalcoholic steatohepatitis (NASH), dyslipidemia, etc., due to its activities of fat decomposition and β-oxydation in the liver.
One of the glucagon derivatives, glucagon-like peptide-1 (GLP-1), is under development as a therapeutic agent for treating hyperglycemia in patients with diabetes. GLP-1 has the functions of stimulating insulin synthesis and secretion, inhibiting glucagon secretion, slowing gastric emptying, increasing glucose utilization, and inhibiting food intake.
Exendin-4, prepared from lizard venom and having an amino acid homology of about 50% with GLP-1, was also reported to activate the GLP-1 receptor, thereby improving hyperglycemia in patients with diabetes (J Biol Chem. 1992 Apr. 15; 267 (11): 7402-5). However, anti-obesity drugs containing GLP-1 are reported to show side-effects such as vomiting and nausea.
As an alternative to GLP-1, therefore, much attention has been focused on oxyntomodulin, which can bind to both receptors of the two peptides, GLP-1 and glucagon. Oxyntomodulin is a peptide prepared from a glucagon precursor, pre-glucagon, and has the functions of inhibiting food intake and enhancing satiety of GLP-1, and has lipolytic activity like glucagon, thus increasing its potency in anti-obesity therapy.
However, oxyntomodulin or derivatives thereof have a serious drawback in that an excess amount of the drug should be administered daily because they have low efficacy and a short in vivo half-life.
Additionally, when both activities of GLP-1 and glucagon are present in a single peptide, the activity ratio thereof becomes fixed, and thus it is difficult to use a dual agonist with various ratios. Accordingly, a combined therapy capable of using various activity ratios by adjusting the contents of GLP-1 and glucagon may be more effective. However, for the combined therapy, it is required to improve the physical characteristics of glucagon, which aggregates at a neutral pH and precipitates with time, thus showing poor solubility.
Under these circumstances, the present inventors have developed glucagon derivatives with partial modifications of the amino acid sequence of glucagon for improving the therapeutic effects of glucagon on hypoglycemia and obesity by improving the physical properties of glucagon, and have discovered that these glucagon derivatives, due to the altered pI values which are different from that of native glucagon, have improved solubility and higher stability at a neutral pH and have confirmed that the developed glucagon derivative activates its receptors in in vitro assay, thereby completing the present invention.